You can pass the entire hash as a hash reference. This would also make things more efficient. Here is the sample code:

my %hash_outside;
$hash_outside{'first'} = 'first value';
$hash_outside{'second'} = 'second value';

sub blah {
  my %hash = %{ +shift; };
  foreach my $k (keys %hash) {
    print "$k -> " . $hash{$k} . "\n";
  }
}

&blah(\%hash_outside);
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Here you pass a hash reference to the sub by appending a backslash ( \%hash_outside ). First line in the sub dereferences the reference to the hash so you can use it as a normal hash.

You could also look at perlref documentation to find out more about references.